Regulatory limits on cyanide in wastewater effluents are becoming more stringent by government regulations and in some states the limits have reached 0.1 mg/l total cyanide.
There are many industrial sources of aqueous cyanide wastes such as from electroplating, steel and coke operations and the manufacture of chemicals. Many naturally occurring hydrocarbon oils such as petroleum, shale oil, tar sand oils and their fractions contain nitrogen compounds which react under selected conditions with metals such as iron and carbon to form metal cyanide complex compounds. Reaction conditions which favor formation of such metal cyanides include a temperature of 700.degree. F. and higher in a reducing atmosphere. These formed cyanides are slightly soluble in water and are found in various foul water streams of a refinery operation in admixture with other undesirable reaction products such as phenol and hydrogen sulfide. Metal cyanide complex compounds are formed in the cracking operations such as fluid catalytic cracking, coking, and hydrocracking operations of a refinery operation, and such formed cyanides end up in some considerable measure in the sour water product stream of the refinery operation.
The subject of water treatment and particularly wastewater of the chemical and petroleum refining industry has been investigated by many researchers in the field. For example, an article entitled "Selective Removal of Cyanide from Industrial Waste Effluents with Ion-Exchange Resins" by N. L. Avery and W. Fries was published in Ind. Eng. Chem. Prod. Res. Dev., Vol. 14, No. 2, 1975. Another pertinent review article on the refinery cyanide problem is entitled "Refinery Cyanides: A Regulatory Dilemma" by R. G. Kung, J. P. Casey and J. E. Huff, published in Hydrocarbon Processing, October 1978. A prior art patent of particular interest on the subject is that of U.S. Pat. No. 3,990,971 issued Nov. 9, 1976.
Up to the present disclosure, there has been no low cost effective process for the disposal of cyanides in refinery wastewaters. The method and process of this invention provide a solution to this dilemma.